Chamber effluent monitoring system and semiconductor processing system comprising absorption spectroscopy measurement system, and methods of use

ABSTRACT

Provided is a novel chamber effluent monitoring system. The system comprises a chamber having an exhaust line connected thereto. The exhaust line includes a sample region, wherein substantially all of a chamber effluent also passes through the sample region. The system further comprises an absorption spectroscopy measurement system for detecting a gas phase molecular species. The measurement system comprises a light source and a main detector in optical communication with the sample region through one or more light transmissive window. The light source directs a light beam into the sample region through one of the one or more light transmissive window. The light beam passes through the sample region and exits the sample region through one of the one or more light transmissive window. The main detector responds to the light beam exiting the sample region. The system allows for in situ measurement of molecular gas impurities in a chamber effluent, and in particular, in the effluent from a semiconductor processing chamber. Particular applicability is found in semiconductor manufacturing process control and hazardous gas leak detection.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/711,781,filed Sep. 10, 1996 now U.S. Pat. No. 5,963,336; which is acontinuation-in-part of application Ser. No. 08/634,449, filed Apr. 18,1996 now abandoned; and claiming benefit of provisional application Ser.No. 60/005,013, filed Oct. 1, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel chamber effluent monitoringsystem and a semiconductor processing system which include an absorptionspectroscopy measurement system for measuring a gas phase molecularspecies. The present invention also relates to a method of detecting agas phase molecular species within the inventive chamber effluentmonitoring system and inventive semiconductor processing system.

2. Description of the Related Art

In the manufacture of semiconductor integrated circuits (ICs), it isimportant to have an extremely low partial pressure of molecularimpurities in the processing chamber. In particular, water vapor isespecially detrimental to the devices fabricated in the processingtools. For example, water vapor must be eliminated or minimized in analuminum etching chamber in order to achieve reproducible etchingprocesses. Also, when subjected to water vapor during processing,corrosion of the device metallization layers is accelerated,substantially reducing product yield.

Molecular impurities may be introduced into the processing chamber in anumber of ways. For example, molecular impurities may be present in theprocess gases introduced into the chamber during processing. Also,molecular impurities such as moisture are present in the air to whichthe chamber is exposed during maintenance of the processing tool. Airand water may also be introduced into the processing chamber whenever asubstrate is introduced into the chamber. Molecular impurities may alsobe released from the substrates themselves after introduction into theprocess chamber or may result from the process conditions themselves.For example, during plasma processing and rapid thermal processing,molecular impurities may take the form of reaction byproducts or, as inthe case of water vapor, may be released from substrate and chambersurfaces upon heating.

Molecular impurities which are introduced into the process chamber witha substrate are typically removed by purging the chamber with a puregas, by evacuating the chamber, or by a series ofpressurization-evacuation cycles.

In the case of chamber evacuation, the base pressure in the chamber isused as a measure of the extent of removal of the molecular impurities.Conversely, when relying on the chamber purge technique, the chamber isfilled with a pure gas for a period of time which is usually determinedby the operator's experience.

The extent of removal of atmospheric contamination from the processingchamber can also be determined by the measurement of water vaporconcentration in the chamber. Such a technique is particularly useful inthe case of contamination resulting from exposing the processing chamberto the outside atmosphere during maintenance and from introducing asubstrate into the chamber. Water vapor can adhere to the surfacesinside a processing chamber as well as to the surface of the substrate.It is present in the atmosphere in an amount of from about 1-2, and isgenerally the most difficult atmospheric constituent to remove byevacuation or purging.

In state-of-the-art production facilities, particle monitors are oftenused to monitor particulate contamination in situ. It is known todispose particle monitors in the exhaust line of processing tools. (See,e.g., P. Borden, Monitoring Vacuum Process Equipment: In SituMonitors--Design and Specification," Microcontamination, 9(1), pp. 43-47(1991)). While such particle monitors may be useful for tracking processevents which result in the generation of particles, they cannot be usedto monitor molecular concentrations.

Among the analysis tools which can be used in the measurement ofmolecular contamination is one type of mass spectrometer, usuallyreferred to as a residual gas analyzer (RGA). (See, e.g., D. Lichtman,Residual Gas Analysis: Past, Present and Future, J. Vac. Sci. Technol.,A 8(3) (1990)). Mass spectrometers generally require pressures in therange of about 10⁻⁵ torr, whereas the operating pressures ofsemiconductor processing tools are often at pressures in the range offrom about 0.1 to 760 torr. Consequently, mass spectrometers requiresampling systems and dedicated vacuum pumps. Mass spectrometers aregenerally both expensive and not compact in construction. Moreover, thedifferentially pumped chamber in which the mass spectrometer is housedcontributes a high level of residual water vapor which is difficult toremove and which severely limits the sensitivity of the massspectrometer for water vapor measurement.

Optical emission spectroscopy is widely used for monitoring plasmaprocesses. In principle, optical emission spectroscopy can be used tomonitor molecular contamination in the processing tool. However, theoptical emission spectrum is very complicated, and this method cannot beused in non-plasma processes.

Other spectroscopic techniques have been widely used in researchsituations to study process chemistry. (See, e.g., Dreyfus et al.,Optical Diagnostics of Low Pressure Plasmas, Pure and Applied Chemistry,57(9), pp. 1265-1276 (1985)). However, these techniques generallyrequire specially modified process chambers and have not generally beenapplied to the study of contamination. For example, the possibility ofin situ moisture monitoring by intracavity laser spectroscopy has beenmentioned generally in a review of that technique. (See, e.g., G. W.Atkinson, High Sensitivity Detection of Water via Intracavity LaserSpectroscopy, Microcontamination, 94 Proceedings Canon Communications(1994)).

Finally, conventional gas analyzers have been applied to in situmoisture measurement, usually for processes running at or close toatmospheric pressure. (See, e.g., Smoak et al., Gas Control Improves EpiYield, Semiconductor International, pp. 87-92 (June 1990)). According tosuch techniques, a portion of the process gas is extracted into a probewhich then delivers the sample to the analyzer. However, use of a probeis undesirable in the measurement of moisture since moisture tends toadsorb on the surfaces of the probe. Moreover, this approach is oftenimpractical as it requires considerable space to accommodate theconventional gas analyzers. It is well known that free space inside asemiconductor fabrication cleanroom is typically at a minimum.

A method for measuring the instantaneous moisture concentration anddrydown characteristics of a processing environment is disclosed in U.S.Pat. No. 5,241,851, to Tapp et al. According to this method, a moistureanalyzer alternately samples the effluent from a process chamber and thegas generated by a standard gas generator. The output of the standardgas generator is adjusted until the analyzer indicates no differencebetween the effluent and standard gas streams. Because the moisturecontent in the output of the standard gas generator is known, the levelin the effluent stream can be determined. This system, however, isinconvenient and complicated as it requires a standard gas generator andcomplicated piping to effect switching between the effluent and standardgas streams. Moreover, there is a risk of backflow from the standard gasgenerator to the process chamber, resulting in contamination.

To meet the requirements of the semiconductor processing industry and toovercome the disadvantages of the prior art, it is an object of thepresent invention to provide a novel chamber effluent monitoring system,and in particular a novel semiconductor processing system, whichincludes an absorption spectroscopy system for detecting gas phasemolecular impurities, which will allow for accurate, instantaneous andin situ determination of gas phase molecular impurities in asemiconductor processing tool.

It is a further object of the present invention to provide a method ofdetecting gas phase molecular species within the inventive chambereffluent monitoring and semiconductor processing systems.

Other objects and aspects of the present invention will become apparentto one of ordinary skill in the art on a review of the specification,drawings and claims appended hereto.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a chamber effluentmonitoring system is provided. The system comprises a chamber having anexhaust line connected thereto. The exhaust line includes a sampleregion, wherein substantially all of a chamber effluent also passesthrough the sample region.

The system further comprises an absorption spectroscopy measurementsystem for detecting a gas phase molecular species. The measurementsystem comprises a light source and a main detector in opticalcommunication with the sample region through one or more lighttransmissive window. The light source directs a light beam into thesample region through one of the one or more light transmissive window,and the light beam passes through the sample region and exits the sampleregion through one of the one or more light transmissive window. Themain detector responds to the light beam exiting the sample region.

In a second aspect of the invention, a semiconductor processing systemis provided. The semiconductor processing system comprises a processingchamber for processing a semiconductor substrate. The processing chambercomprises an exhaust line connected thereto. The exhaust line includes asample region, wherein substantially all of a chamber effluent passesthrough the sample region.

The processing system further comprises an absorption spectroscopymeasurement system for measuring a gas phase molecular species asdescribed above with reference to the chamber effluent monitoringsystem.

A third aspect of the invention is a method of detecting a gas phasemolecular species in a chamber effluent. In the inventive method, achamber is provided which has an exhaust line connected thereto. Theexhaust line includes a sample region. Substantially all of a chambereffluent is removed from the chamber through the exhaust line and ispassed through the sample region.

A gas phase molecular species is detected by an absorption spectroscopymethod by directing a light beam from a light source into the sampleregion through one or more light transmissive window. The light beampasses through the sample region and exits the sample region through oneof the one or more light transmissive window, and the light beam exitingthe cell through one of the one or more light transmissive window isdetected.

The novel systems and methods permit accurate, instantaneous and in situdetection of gas phase molecular species in a chamber effluent.Particular applicability can be found in semiconductor manufacturingprocess control and in hazardous gas leak detection. For example, thetime dependent moisture concentration and drydown characteristics of asemiconductor process environment can be monitored.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become apparent fromthe following detailed description of the preferred embodiments thereofin connection with the accompanying drawings in which like numeralsdesignate like elements, and in which:

FIGS. 1A, 1B and 1C are side-sectional views of chamber effluentmonitoring systems according to the present invention;

FIGS. 2A and 2B are cross-sectional views of chamber effluent monitoringsystems according to the present invention;

FIG. 3 is a graph of water vapor concentration versus etching processtime in accordance with Example 1;

FIG. 4 is a graph of carbon monoxide concentration versus etchingprocess time in accordance with Example 2; and

FIG. 5 is a cross-sectional view of chamber effluent monitoring systemsaccording to further aspects of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The above objectives of the present invention have been realized throughthe use of a spectroscopic method to measure molecular gas phase speciesin a chamber effluent, wherein substantially the entire flow of effluentgas from the chamber is directed through a spectroscopic sample region.In this way, measurements which follow changes in the actual impuritycontent in the effluent can be made very quickly.

As used herein, the terms "molecular gas phase species," "molecularimpurity" and "contamination" are considered equivalent terms, and referto a molecular gas or vapor species which is the object of theabsorption spectroscopy measurement. Also, as used herein, the term"substantially the entire flow of effluent" means about 90-100% byvolume of the total effluent flow from the chamber.

The invention will now be described with reference to FIGS. 1A and 2A,which illustrate side-sectional and cross-sectional views, respectively,of an inventive chamber effluent monitoring system.

System 1 comprises a semiconductor processing chamber 2, inside which asemiconductor substrate 3 is disposed on a substrate holder 4. A gasinlet 5 is provided for delivering a process gas or plural gases toprocessing chamber 2. Effluent from processing chamber 2 is exhaustedthrough an exhaust opening 6 in processing chamber 2 and through anexhaust line 7 which can be connected to a vacuum pump, a fan or ascrubber system 20.

According to one aspect of the invention, the processing system issuitable to run vacuum processes, such as etching, sputtering, ionimplantation or chemical vapor deposition (CVD) processes. In such acase, processing chamber 2 is a vacuum chamber, and a vacuum pump (notshown) can be connected to the exhaust line 7. The vacuum pump can beconnected to another pump and/or to a gas scrubber (not shown). Examplesof vacuum pumps which may be employed in these processes are mechanicalrotary and booster pumps, diffusion pumps, cryogenic pumps, sorptionpumps and turbomolecular pumps. Alternatively, the processing system canrun processes such as atmospheric pressure CVD, wherein processingchamber 2 is held at about atmospheric pressure with a slight vacuum.

The processes often call for reactive or nonreactive (inert) gas specieswhich can be in a plasma- or non-plasma state. Examples of reactivegases which can be used in the inventive system include SiH₄, HCl andCl₂, provided the moisture level is less than 1000 ppm. However, thereactive gases are not limited to these. Any inert gas such as, e.g.,O₂, N₂, Ar and H₂ can be used in the inventive system.

In order to detect and measure molecular gas phase impurityconcentrations in the processing tool, the inventive semiconductorprocessing system further includes an absorption spectroscopymeasurement system 8 for measuring a gas phase molecular species. Theabsorption spectroscopy measurement system comprises a light source 9and a detector 10, which can be a photodiode, in optical communicationwith a sample region 11 in exhaust line 7.

Any molecular impurity of interest can be detected, subject only to theavailability of a suitable light source. For example, water vapor,nitric oxide, carbon monoxide and methane or other hydrocarbons can bedetected by measuring the attenuation of light from a diode laser sourcewhich emits light of a wavelength characteristic of the impurity.

Laser light sources which emit light in spectral regions where themolecules of interest absorb most strongly lead to improvements inmeasurement sensitivity. In particular, light sources which emit atwavelengths longer than about 2 μm are preferred, since many of themolecular impurities of interest have strong absorption bands in thisregion.

Any suitable wavelength-tunable light source can be used. Of thecurrently available light sources, diode laser light sources arepreferred because of their narrow linewidth (less than about 10⁻³ cm⁻¹)and relatively high intensity (about 0.1 to several milliwatts) at theemission wavelength.

Examples of diode lasers include Pb-salt and GaAs-type diode lasers. ThePb-salt-type laser requires cryogenic temperatures for operation andemits infrared light (i.e., wavelength greater than 3 μm), while theGaAs-type diode laser can operate at close to room temperature and emitsin the near infrared region (0.8-2 μm).

Recently, diode lasers which include Sb in addition to GaAs (or otherpairs of III-V compounds such as AsP) have been described (see,"Mid-infrared wavelengths enhance trace gas sensing," R. Martinelli,Laser Focus World, March 1996, p. 77). These diodes emit light of awavelength greater than 2 μm while operating at -87.8° C. While such alow temperature is not convenient, it compares favorably with thecryogenic temperatures (less than -170° C.) required by Pb-salt lasers.Operation of similar lasers at 4 μm and 12° C. has also been reported(see, Lasers and Optronics, March 1996). Diode lasers of the abovedescribed type will most preferably operate at temperatures of at least-40° C. Use of a thermoelectric cooler for temperature control at suchtemperatures makes these light sources less complicated than the lowertemperature diode systems. To make use of these lasers more desirable,improvement in the optical properties over current levels is important.For example, single mode diodes (i.e., diodes whose emission at fixedtemperature and drive current is at a single wavelength with emission atother wavelengths at least 40 dB less intense) should be available.

Suitable light sources for use in the invention are not limited to theabove described diode lasers. For example, other types of lasers whichare similarly sized and tunable by simple electrical means, such asfiber lasers and quantum cascade lasers, are envisioned. The use of suchlasers as they become commercially available is envisioned.

Light beam 12 which is generated by the described light source 9 istransmitted into sample region 11 through at least one lighttransmissive window 13, which can be disposed in the wall of exhaustline 7. The measurement system can be configured such that light beam 12is reflected by a light reflective surface 14 within the sample regionand exits sample region 11 through the same window it enters the sampleregion through. Alternatively, the windows through which the light beamenters and exits the sample region can be different and can be disposedon different sides of the exhaust line, for example, as illustrated inFIG. 1B, which shows light beam 12 passing through first lighttransmissive window 13a before entering the sample region 11, and thelight beam passing through second light transmissive window 13b afterpassing through the sample region. In this exemplary embodiment, thelight path between the first and second light transmissive windows issubstantially linear. The measurement system can also be configured suchthat the light beam passes straight through the sample region from alight inlet window through a light exit window without being reflectedin the sample region.

Light reflective surface 14 can be formed either separate from orintegral with a wall of exhaust line 7. Light reflective surface 14 ispreferably a polished metal. As a high reflectivity of this surface isdesirable, the surface can be coated with one or more layers of areflective material such as gold, other metallic layers or a highlyreflective dielectric coating in order to enhance the reflectivitythereof. Moreover, to minimize the adverse effects created by depositsformed on the light reflective surfaces, a heater for heating the lightreflective surface can also be provided.

With reference to FIG. 1C, when the spectroscopy measurement is made ina portion of the exhaust line which is not connected to the chamber by astraight line, but rather is connected to the chamber after a bend inthe line, it has been determined that removal of a small portion of theexhaust at the bend is particularly advantageous in that the fluiddynamics in the measurement region are enhanced considerably. A bend inthe exhaust line upstream from the sample region results in eddies whichare relatively slow to respond to upstream concentration changes.

In such a case, a fluid stabilizing amount of exhaust can be removedthrough fluid stabilization line(s) 15. In so doing, the eddies can beeffectively eliminated or minimized. The amount of effluent removed fromthrough fluid stabilization line 15 is less than about 10% by volume ofthe total effluent flow from the chamber.

In reference to FIGS. 2A, the absorption spectroscopy measurement system8 can further include at least one first mirror 16 for reflecting lightbeam 12 from light source 9 through light transmissive window 13 intosample region 11, and at least one second mirror 17, 18 for reflectinglight beam 12 exiting sample region 11 to main detector 10. Mirror 16 ispreferably curved in order to collimate the light beam as the light fromthe diode laser source is divergent. Likewise, mirrors 17, 18 arepreferably curved in order to focus the parallel light beam on detector10.

In a further embodiment of the invention, illustrated in FIG. 2B, theangle of light transmissive window 13 can be adjusted such that theincident angle of the laser light can be increased or decreased awayfrom an angle normal to the window. This feature is particularlyadvantageous because reflection of the laser light back to the laser canbe adjusted and minimized. Such back reflection can both increase lasernoise (e.g., by feedback into the cavity) or lead to interferencefringes (e.g., by forming an etalon with the laser facets) which reducemeasurement sensitivity.

Disposing window 13 at an angle conveys a further advantage in that asecond detector 19 can be conveniently utilized for detection of thereflected portion of the incident light beam. It should be noted thatthe figures are not drawn to scale, and in practice window 13 can bemade as small as required. Also, the angle between the incident lightbeam and the reflected light beam from mirror 14 is, in practice,smaller than indicated. Thus, the importance of angling the window 13 isgreater than might appear from a very casual inspection of FIGS. 2A and2B.

Light transmissive window 13 can additionally be provided with a coatinglayer on a surface opposite the surface facing the sample region forreflecting a portion of light beam 12. Subtracting the signal due to thereflected portion of the beam from that of the transmitted portion canresult in more accurate absorption measurements. Among the commerciallyavailable coating materials, metallic coatings are preferred. Suitablecoated windows are commercially available from various suppliers such asOriel, Melles Griot, and Newport.

A second detector 19, which can also be a photodiode, for measuring aportion 20 of the light beam which is reflected from light transmissivewindow 13 as well as means for subtracting this reference signal from ameasurement obtained by main detector 10 can optionally be provided inthe system. An operational amplifier in a configuration such asdescribed in the literature (See, e.g., Moore, J. H. et al., BuildingScientific Apparatus, Addison Wesley, London, (1983)) can act as themeans for subtracting the reference signal.

The reflected light does not show any absorption by the molecules ofinterest in the sample region, and therefore provides a referencesignal. By subtracting the reference signal from that of the light whichpasses through the cell (which is measured by the main detector),variations in the light source can be compensated for. This also allowsfor enhanced sensitivity to signal changes due to the molecular speciesin the processing chamber 2. While "dual beam" techniques usingsubtraction of a reference beam are well-known, they usually require adedicated beam-splitter, i.e., an optical element whose only function isto divide the light beam. According to the present invention, theentrance window to the chamber can provide this function without theneed for any additional components. The ratio of transmitted toreflected light at this window can be controlled by use of anappropriate coating for the window.

The light source is preferably a diode laser maintained at a preciselycontrolled temperature. The temperature of the diode laser is generallycontrolled with a precision of at least plus or minus 0.1° C. Suitablediode lasers and temperature controllers are well known in the art andare available from several manufacturers. Lead salt lasers are availablefrom the Laser Analytics Division of Laser Photonics Corp., and GaAslasers are available from Sensors Unlimited, Inc. A suitable temperaturecontroller is the Lake Shore DRC-910A temperature controller (forcryogenic temperatures) or any of several models from ILX Lightwave,Inc. for near room temperature operation.

Light source electronics control the current applied to the diode lasersuch that the diode laser emits light of a specific wavelength which isabsorbed by the molecular impurity desired to be measured. As currentapplied to the laser diode increases, wavelength increases or decreasesdepending on the diode type. Laser current controllers are known in theart and commercially available. A suitable controller is the ILXLightwave LDX-3620.

A detector, such as a photodiode, responds to light of the samewavelength as emitted by the diode laser. Suitable detectors are knownin the art and commercially available, such as the Graseby HgCdTe Model1710112 for infrared detection, or the EG&G InGaAs C30641 for nearinfrared detection, with a 10 MHz bandwidth amplifier. Detector 10responds to light beam 12 which is reflected from a surface within theexhaust line and exits the sample region through one of the one or morelight transmissive window 13. Detector electronics receive the outputfrom the detector and generate an output which is related to theabsorbance of light at the desired wavelength. The absorbance, i.e., theratio of the detected light intensity in the presence of the molecularimpurities of interest to the intensity which would be observed in theirabsence, can be converted into a concentration of the molecularimpurities by a computer using known calibration data.

Various methods for controlling the wavelength of the light emitted bythe diode laser can be used. For example, the laser wavelength may belocked to the desired value by a feedback system or may be repetitivelyswept over a region which includes the desired wavelength in order togenerate a spectrum. Subsequent spectra may be averaged to improvesensitivity. Both of these techniques are known. (See, e.g., Feher etal., Tunable Diode Laser Monitoring of Atmospheric Trace GasConstituents, Spectrochimica Acta, A 51, pp. 1579-1599 (1995) andWebster et al., Infrared Laser Absorption: Theory and Applications,Laser Remote Chemical Analysis, R. M. Measuews (Ed.), Wiley, New York(1988)). A further method for stabilizing wavelength is disclosed incopending application, Ser. No. 08/711,780, filed on even date herewith,Attorney Docket No. 016499-205, which is hereby incorporated byreference.

Further improvements in sensitivity can be achieved by modulating thediode current and wavelength and demodulating the detector signal at themodulation frequency or one of its higher harmonics. This technique isknown as harmonic detection spectroscopy. (See, Feher et al., TunableDiode Laser Monitoring of Atmospheric Trace Gas Constituents,Spectrochimica Acta, A 51, pp. 1579-1599 (1995) and Webster et al.,Infrared Laser Absorption: Theory and Applications in Laser RemoteChemical Analysis, R. M. Measuews (Ed.), Wiley, New York (1988)).

As disclosed in copending application, Ser. No. 08/711,646, filed oneven date herewith, Attorney Docket No. 016499-203, which is herebyincorporated by reference, in a particularly effective harmonicdetection absorption system, the light source modulation amplitude canbe set to a value which approximately maximizes the value of a harmonicsignal at the center of the absorption feature being detected. In thissystem, the light source and detector are contained within a chamberwhich is isolated from the sample region, and the chamber pressure iscontrolled to a pressure greater than atmospheric pressure. Bypressurizing the chamber, the detected signal can be maximized, therebyproviding accurate measurements in a sample as low as in the parts perbillion (ppb) range.

In another embodiment of the invention, a plurality of mirrors (or onemirror having multiple faces) can be disposed within the exhaust line 7.This allows the light beam to pass through the sample region a pluralityof times. By increasing the effective pathlength in this manner,sensitivity of the measurement system is thereby enhanced.

Various forms of multipass optics are disclosed in copending applicationSer. No. 08/711,504, filed on even date herewith, Attorney Docket No.016499-204, which is hereby incorporated by reference. As disclosed inthis copending application, multipass cells are able to improvesensitivity of the measurement system by extending the effectivepathlength the light beam travels. Among these cells, the planarmultipass cell can be made arbitrarily small in directions parallel andperpendicular to the plane of propagation of the light. Because of itssize, the planar multipass cell is particularly well suited for use inexisting semiconductor processing tools.

The particular cell featured in that application is a polygonal planarmultipass cell. The cell comprises a sample region circumscribed by aplurality of walls with light reflective surfaces. As a result of theregular shape, the light beam can be reflected by each wall prior toexiting the cell. Because the light beam can remain in the same plane,the size of the cell can be kept to a minimum.

The following example illustrate that the systems and methods of theinvention are particularly beneficial in the detection of gas phasemolecular species.

EXAMPLE 1

As described below, moisture concentration in a semiconductor processingsystem during etching is monitored, using the operating proceduredescribed below.

As the semiconductor processing system, an Applied Materials Precision5000 plasma etching system is used in conjunction with a TDLASmeasurement system. The measurement system is set up for water vapormeasurement to determine the drydown characteristics of the processingchamber.

The measurement system sample region is disposed in the exhaust line ofthe etching tool. The light transmissive inlet and outlet windows aredisposed directly across from each other in the walls of the exhaustline, with the sample region disposed therebetween, such that the lightemitted by the laser diode passes straight through the inlet window tothe outlet window.

The diode is manufactured by Sensors Unlimited Inc., and is composed ofInGaAsP/InP. The diode is fabricated in order to emit light in thewavelength region including 1.3686 micrometer where a strong absorptionby water vapor occurs. The diode is of the distributed feedback (DFB)type, ensuring single mode emission, i.e., to ensure that the diodeemits at a single frequency, as described in M. Feher et al,Spectrochimica Acta A 51 pp. 1579-1599 (1995). The diode is mounted on athermoelectric cooler which is controlled to 25° C. by a Hytek 5610subminiature proportional temperature controller. The laser current iscontrolled by an ILX Lightwave ILX 3620.

The diode is placed at the focus of a 0.5 inch diameter off-axisparaboloid mirror which collimates the diode laser beam. The mirror hasa polished aluminum surface. The detector is an EG&G C30642 which is a 2mm active diameter InGaAs photodiode. The detector output is amplifiedby an Analog Modules Inc. pre-amplifier. The system is extremelycompact, and (except for the current controller) can be accommodated ina cube about 6 inches on each side.

The wavelength of the light emitted by the laser diode is locked to thecharacteristic value (i.e., 1.3686 μm) using a feedback signal to thelaser diode. To properly lock onto the wavelength, a signalcorresponding to the third derivative of the absorption signal is used.Moisture measurements are initiated upon entry of the substrate into theprocessing chamber and are terminated upon completion of the process,with measurements being averaged over one second intervals. The data areinstantaneously calculated, with the results being fed back to theetching tool process controller.

After loading the semiconductor substrate into the processing chamber,the system is evacuated until the water vapor partial pressure is 20mtorr. At this point, 30 scam BCl₃, 40 scam Cl₂, 250 scam He and 9.4scam CHCl₃ are introduced into the processing chamber. After one minute,the gas flows are shut off and the moisture level gradually recovers toapproximately its previous level following reaction with residual BCl₃.

FIG. 3 is a graph of water vapor pressure versus processing time. Themoisture partial pressure drops below detectable levels because of therapid reaction of BCl₃ With water vapor as follows:

    2BCl.sub.3 +3H.sub.2 O=B.sub.2 O.sub.3 (solid)+6HCl

Thus, adding BCl₃ too early in the process, when the moisture partialpressure is too high, is disadvantageous since an excessive quantity ofparticles will be formed. Particles are well-known to have deleteriouseffects on the semiconductor devices. On the other hand, the presence ofwater vapor during several etch processes, such as aluminum etching, isintolerable. BCl₃ is therefore necessary in order to eliminate the lastvestiges of water vapor. The inventive system can be used to determinewhen the moisture partial pressure is sufficiently low to permit BCl₃addition and also to verify that the addition of BCl₃ is sufficient tocompletely remove vestigial water vapor.

EXAMPLE 2

Using the same etching tool described above in reference to Example 1,CO is monitored in a plasma ASH process wherein photoresist from anetched substrate is stripped. In the measurement system, a Pb-salt diodemanufactured by Laser Photonics Corp. is mounted in a Laser Analyticsliquid nitrogen-cooled coldhead. A one inch diameter, aspheric,antireflective coated, F/1 ZnSe lens is used to collimate the beam. Thedetector is a Graseby HgCdTe Model 1710112, with a 10 MHz bandwidthamplifier. Laser current is controlled by an ILX Lightwave LDX-3620, andthe temperature is controlled by a Lake Shore DRC-910A controller. Thewavelength of the light emitted by the laser diode is locked to thecharacteristic value for CO, i.e., 4.7 μm, using a feedback signal tothe laser diode. A signal corresponding to the third derivative of theabsorption signal is used.

After loading the semiconductor substrate into the etching chamber, O₂at a flow rate of 60 sccm is introduced into the chamber. The pressureis maintained at 1.5 Torr during processing, and the CO measurements areperformed throughout processing. Measurements are averaged over onesecond intervals.

The results from the CO measurement are set forth in FIG. 4, showing COvapor pressure versus processing time. The graph indicates that theendpoint of the process occurs after about 6 minutes, at which point theCO in the processing chamber drops off.

The above examples show that the inventive system and method are wellsuited for monitoring gas phase molecular species in an exhaust line.

In addition to the above applications, the invention is particularlyapplicable to use in a load-lock chamber. Whenever a wafer is introducedinto a semiconductor processing chamber, it is generally first placed ina load-lock chamber, which is purged and/or vacuum cycled in order toremove atmospheric air and other contaminants. The wafer is thentransferred from the load-lock chamber to the process chamber itself.The extent of purging and/or vacuum cycles required may be determined bythe pressure attained in the vacuum cycle. However, this is not aspecific measurement and does not indicate whether the residual pressureis primarily due to water vapor (usually a result of substrate exposureto air), or to other species outgassing from the substrate (usually fromprevious process steps). Thus, it is particularly beneficial to monitorwater vapor in load-lock chambers. Such a method is especially usefulfor load-locks relying solely on purging, since vacuum measurement isnot feasible.

By disposing a diode laser system on the exhaust line of a load-lockchamber, it is possible to measure water vapor in the load lock effluentafter purge cycling. If the required moisture level in the process isknown, the purging time can be optimized to be just sufficient toprovide the requisite purity. As transfer steps between processes areknown to account for a significant fraction of available process chambertime in the semiconductor industry, significant cost advantages can berealized by this procedure.

In a similar way, a moisture sensor placed on the exhaust of any chambercan be used to optimize the length of an initial purge or vacuum cycle,which is often used to eliminate atmospheric constituents after loadingwafers from the clean room, a previous process step, a load-lockchamber, or a transfer chamber.

While the invention has been described in reference to a semiconductorprocessing tool, persons of ordinary skill in the art will readilyappreciate that the inventive system can also be adapted to a variety ofdifferent applications. For example, it is envisioned that the chambereffluent monitoring system can also be used as a safety device indealing with hazardous gases or vapors. In particular, and withreference to FIG. 5, the chamber effluent monitoring system 8 can beused to monitor the exhaust from a chamber 21 which chamber is a gascylinder cabinet, a semiconductor manufacturing cleanroom, or a vacuumpump housing.

It is well known that in the IC manufacturing processes, a multitude ofhazardous and toxic gases are required. Generally, such gases are keptin cabinets which are continuously evacuated. The cabinet exhaust, i.e.,effluent, is drawn through an exhaust line usually to a scrubber system.The inventive chamber effluent monitoring system is particularly wellsuited for use with these gas cabinets. By disposing an absorptionspectroscopy measurement system 8 in the cabinet exhaust 7, a leakdetection system providing instantaneous feedback is provided. Inparticular, a system for detection of HF which has an absorption at awavelength of 1330 nm, coincident with relatively convenient InGaAsPdioxide emission, is envisioned.

This embodiment is preferably used in conjunction with a visual and/oraudio alarm system 22. The alarm system 22 can be activated upon thehappening of a certain event, such as the detected absorption or gasconcentration exceeding a predefined limit. In addition, the detectorcan be connected to a valve control system which will automaticallyclose the gas cylinder or other valve(s) to stop the flow of gas. Thoseskilled in the art will readily be able to design and integrateappropriate alarm systems and controls in the inventive system by use ofwell known devices, circuits and/or processors and means for theircontrol. Further discussion of this matter is omitted as it is deemedwithin the scope of persons of ordinary skill in the art. In a furtherembodiment of the invention, the chamber effluent monitoring system canbe used to monitor the environment of a vacuum pump housing.

In another embodiment of the invention, the chamber effluent monitoringsystem can be applied to the monitoring of cleanroom environments.Because the air exhausted from the cleanroom is generally returned tothe cleanroom, hazardous gas leaks or the presence of hazardous vaporsin the cleanroom are especially problematic. Therefore, use of anabsorption spectroscopy measurement system in the cleanroom exhaust canprovide a particularly advantageous leak detection system. As discussedabove in reference to the gas cabinets, this system can be used inconjunction with an alarm system.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made, and equivalentsemployed, without departing from the scope of the appended claims.

What is claimed is:
 1. A chamber effluent monitoring system,comprising:a chamber having an exhaust line connected thereto, theexhaust line including a sample region, wherein substantially all of achamber effluent also passes through the sample region; an absorptionspectroscopy measurement system for detecting a gas phase molecularspecies, comprising a laser light source and a main detector in opticalcommunication with the sample region through one or more lighttransmissive window, the light source directing a light beam into thesample region through one of the one or more light transmissive window,wherein the light beam passes through the sample region and exits thesample region through one of the one or more light transmissive window,and the main detector responding to the light beam exiting the sampleregion.
 2. The chamber effluent monitoring system according to claim 1,wherein the absorption spectroscopy system is a tunable diode laserabsorption spectroscopy system.
 3. The chamber effluent monitoringsystem according to claim 1, wherein the absorption spectroscopy systemis a harmonic detection absorption spectroscopy system.
 4. The chambereffluent monitoring system according to claim 3, wherein the harmonicused is a second harmonic.
 5. The chamber effluent monitoring systemaccording to claim 3, wherein the harmonic used is a fourth harmonic. 6.The chamber effluent monitoring system according to claim 1, furthercomprising a second detector for providing a reference signal in aportion of the light beam which is reflected by the one of the one ormore light transmissive window through which the light beam passes intothe sample region.
 7. The chamber effluent monitoring system accordingto claim 6, further comprising means for subtracting a reference signalprovided by the second detector from a measurement obtained by the maindetector.
 8. The chamber effluent monitoring system according to claim1, wherein the sample region is disposed in the exhaust line between andin communication with the chamber and a vacuum pump, a fan, or ascrubber system.
 9. The chamber effluent monitoring system according toclaim 1, wherein the operation pressure of the processing chamber isabout atmospheric pressure.
 10. The chamber effluent monitoring systemaccording to claim 1, wherein the absorption spectroscopy measurementsystem is adapted to measure a concentration of water vapor.
 11. Thechamber effluent monitoring system according to claim 1, wherein thelight beam passes through a first light transmissive window beforeentering the sample region, and the light beam passes through a secondlight transmissive window after passing through the sample region,wherein a light path from the first and second light transmissive windowis substantially linear.
 12. The chamber effluent monitoring systemaccording to claim 1, wherein the light beam is reflected within thesample region by one or more light reflective surfaces.
 13. The chambereffluent monitoring system according to claim 1, wherein the sampleregion is contained within a measurement cell.
 14. The chamber effluentmonitoring system according to claim 13, wherein the measurement cell isa multipass measurement cell.
 15. The chamber effluent monitoring systemaccording to claim 1, wherein the monitoring system further comprises afluid stabilization line for removing less than about 10% by volume ofthe total effluent flow from the chamber.
 16. The chamber effluentmonitoring system according to claim 1, further comprising an alarmsystem which activates when the detected gas phase molecular speciesreaches a predefined detection limit.
 17. The chamber effluentmonitoring system according to claim 1, wherein the chamber is a gascylinder cabinet.
 18. The chamber effluent monitoring system accordingto claim 17, further comprising an alarm system which activates when thedetected gas phase molecular species reaches a predefined detectionlimit.
 19. The chamber effluent monitoring system according to claim 1,wherein the chamber is a vacuum pump housing.
 20. The chamber effluentmonitoring system according to claim 19, further comprising an alarmsystem which activates when the detected gas phase molecular speciesreaches a predefined detection limit.
 21. The chamber effluentmonitoring system according to claim 1, wherein the chamber is acleanroom.
 22. The chamber effluent monitoring system according to claim21, further comprising an alarm system which activates when the detectedgas phase molecular species reaches a predefined detection limit.
 23. Asemiconductor processing system, comprising:a processing chamber forprocessing a semiconductor substrate, the chamber having an exhaust lineconnected thereto, the exhaust line including a sample region, whereinsubstantially all of a chamber effluent also passes through the sampleregion; an absorption spectroscopy measurement system for detecting agas phase molecular species, comprising a laser light source and a maindetector in optical communication with the sample region through one ormore light transmissive window, the light source directing a light beaminto the sample region through one of the one or more light transmissivewindow, wherein the light beam passes through the sample region andexits the sample region through one of the one or more lighttransmissive window, and the main detector responding to the light beamexiting the sample region.
 24. The semiconductor processing systemaccording to claim 23, wherein the absorption spectroscopy system is atunable diode laser absorption spectroscopy system.
 25. Thesemiconductor processing system according to claim 23, wherein theabsorption spectroscopy system is a harmonic detection absorptionspectroscopy system.
 26. The semiconductor processing system accordingto claim 25, wherein the harmonic used is a second harmonic.
 27. Thesemiconductor processing system according to claim 25, wherein theharmonic used is a fourth harmonic.
 28. The semiconductor processingsystem according to claim 23, further comprising a second detector fordetecting gas phase molecular species in a portion of the light beamwhich is reflected by the one of the one or more light transmissivewindow through which the light beam passes into the sample region. 29.The semiconductor processing system according to claim 28, furthercomprising means for subtracting a reference signal provided by thesecond detector from a measurement obtained by the main detector. 30.The semiconductor processing system according to claim 23, wherein thesample region is disposed in the exhaust line between and incommunication with the processing chamber and a vacuum pump.
 31. Thesemiconductor processing system according to claim 30, wherein thesemiconductor processing system is selected from the group consisting ofan etching system, a chemical vapor deposition system, an ionimplantation system, a sputtering system and a rapid thermal processingsystem.
 32. The semiconductor processing system according to claim 31,wherein the semiconductor processing system is an etching systemselected from an oxide etch and a metal etch system.
 33. Thesemiconductor processing system according to claim 23, wherein theoperation pressure of the processing chamber is about atmosphericpressure.
 34. The semiconductor processing system according to claim 23,wherein the processing chamber is adapted to contain a plasmaatmosphere.
 35. The semiconductor processing system according to claim23, wherein the processing chamber is adapted to contain a reactive gasatmosphere.
 36. The semiconductor processing system according to claim23, wherein the absorption spectroscopy measurement system is adapted tomeasure a concentration of water vapor.
 37. The semiconductor processingsystem according to claim 23, wherein the light beam passes through afirst light transmissive window before entering the sample region, andthe light beam passes through a second light transmissive window afterpassing through the sample region, wherein a light path from the firstand second light transmissive window is substantially linear.
 38. Thesemiconductor processing system according to claim 23, wherein the lightbeam is reflected within the sample region by one or more lightreflective surfaces.
 39. The semiconductor processing system accordingto claim 23, wherein the sample region is contained within a measurementcell.
 40. The semiconductor processing system according to claim 39,wherein the measurement cell is a multipass measurement cell.
 41. Thesemiconductor processing system according to claim 23, wherein themonitoring system further comprises a fluid stabilization line forremoving less than about 10% by volume of the total effluent flow fromthe processing chamber.
 42. A method of detecting a gas phase molecularspecies in a chamber effluent, comprising the steps of:providing achamber having an exhaust line connected thereto, the exhaust lineincluding a sample region; removing substantially all of a chambereffluent from the chamber through the exhaust line thereby passing theremoved effluent through the sample region; detecting with a maindetector a gas phase molecular species by an absorption spectroscopymethod by directing a light beam from a laser light source into thesample region through one or more light transmissive window, wherein thelight beam passes through the sample region and exits the sample regionthrough one of the one or more light transmissive window, and detectingthe light beam exiting the cell through one of the one or more lighttransmissive window.
 43. The method of detecting a gas phase molecularspecies according to claim 42, wherein the absorption spectroscopymethod is a tunable diode laser absorption spectroscopy method.
 44. Themethod of detecting a gas phase molecular species according to claim 42,wherein the absorption spectroscopy method is a harmonic detectionabsorption spectroscopy method.
 45. The method of detecting a gas phasemolecular species according to claim 44, wherein the harmonic used is asecond harmonic.
 46. The method of detecting a gas phase molecularspecies according to claim 44, wherein the harmonic used is a fourthharmonic.
 47. The method of detecting a gas phase molecular speciesaccording to claim 42, further comprising detecting gas phase molecularspecies in a portion of the light beam which is reflected by the one ofthe one or more light transmissive window through which the light beampasses into the sample region.
 48. The method of detecting a gas phasemolecular species according to claim 47, further comprising subtractinga reference signal provided by a second detector from a measurementobtained by the main detector.
 49. The method of detecting a gas phasemolecular species according to claim 42, wherein the chamber operates atabout atmospheric pressure.
 50. The method of detecting a gas phasemolecular species according to claim 42, wherein the chamber isevacuated by a vacuum pump, a fan, or a scrubber system in communicationwith the exhaust line.
 51. The method of detecting a gas phase molecularspecies according to claim 42, wherein the molecular species is watervapor.
 52. The method of detecting a gas phase molecular speciesaccording to claim 42, wherein the chamber is a semiconductor processingchamber which forms a part of a semiconductor processing system.
 53. Themethod of detecting a gas phase molecular species according to claim 52,wherein the semiconductor processing system is selected from the groupconsisting of an etching system, a chemical vapor deposition system, anion implantation system, a sputtering system and a rapid thermalprocessing system.
 54. The method of detecting a gas phase molecularspecies according to claim 53, wherein the semiconductor processingsystem is an etching system.
 55. The method of detecting a gas phasemolecular species according to claim 52, wherein the processing chambercontains a plasma atmosphere.
 56. The method of detecting a gas phasemolecular species according to claim 52, wherein the processing chambercontains a reactive gas atmosphere.
 57. The method of detecting a gasphase molecular species according to claim 52, wherein the molecularspecies is water vapor.
 58. The method of detecting a gas phasemolecular species according to claim 42, wherein the light beam passesthrough a first light transmissive window before entering the sampleregion, and the light beam passes through a second light transmissivewindow after passing through the sample region, wherein a light pathfrom the first and second light transmissive window is substantiallylinear.
 59. The method of detecting a gas phase molecular speciesaccording to claim 42, wherein the light beam is reflected within thesample region by one or more light reflective surfaces.
 60. The methodfor detecting a gas phase molecular species according to claim 42,wherein the sample region is contained within a measurement cell. 61.The method of detecting a gas phase molecular species according to claim60, wherein the measurement cell is a multipass measurement cell. 62.The method of detecting a gas phase molecular species according to claim42, further comprising removing less than about 10% by volume of thetotal effluent flow from the sample region.
 63. The method of detectinga gas phase molecular species according to claim 42, further comprisingproviding an alarm system which activates when the detected gas phasemolecular species reaches a predefined detection limit.
 64. The methodof detecting a gas phase molecular species according to claim 42,wherein the chamber is a gas cylinder cabinet.
 65. The method fordetecting gas phase molecular species according to claim 64, furthercomprising providing an alarm system which activates when the detectedgas phase molecular species reaches a predefined detection limit. 66.The method of detecting a gas phase molecular species according to claim42, wherein the chamber is a vacuum pump housing.
 67. The method ofdetecting a gas phase molecular species according to claim 66, furthercomprising providing an alarm system which activates when the detectedgas phase molecular species reaches a predefined detection limit. 68.The method of detecting a gas phase molecular species according to claim42, wherein the chamber is a cleanroom.
 69. The method for detecting gasphase molecular species according to claim 68, further comprisingproviding an alarm system which activates when the detected gas phasemolecular species reaches a predefined detection limit.
 70. A chambereffluent monitoring system, comprising:a chamber having an exhaust lineconnected thereto, the exhaust line including a sample region, whereinsubstantially all of a chamber effluent also passes through the sampleregion; an absorption spectroscopy measurement system for detectingwater vapor, nitric oxide, carbon monoxide, or a hydrocarbon, comprisinga light source and a main detector in optical communication with thesample region through one or more light transmissive window, the lightsource directing a light beam into the sample region through one of theone or more light transmissive window, wherein the light beam passesthrough the sample region and exits the sample region through one of theone or more light transmissive window, and the main detector respondingto the light beam exiting the sample region.
 71. The chamber effluentmonitoring system according to claim 70, wherein the absorptionspectroscopy measurement system detects water vapor.
 72. A semiconductorprocessing system, comprising:a processing chamber for processing asemiconductor substrate, the chamber having an exhaust line connectedthereto, the exhaust line including a sample region, whereinsubstantially all of a chamber effluent also passes through the sampleregion; an absorption spectroscopy measurement system for detectingwater vapor, nitric oxide, carbon monoxide, or a hydrocarbon, comprisinga light source and a main detector in optical communication with thesample region through one or more light transmissive window, the lightsource directing a light beam into the sample region through one of theone or more light transmissive window, wherein the light beam passesthrough the sample region and exits the sample region through one of theone or more light transmissive window, and the main detector respondingto the light beam exiting the sample region.
 73. The semiconductorprocessing system according to claim 72, wherein the absorptionspectroscopy measurement system detects water vapor.
 74. A method ofdetecting a gas phase molecular species in a chamber effluent,comprising the steps of:providing a chamber having an exhaust lineconnected thereto, the exhaust line including a sample region; removingsubstantially all of a chamber effluent from the chamber through theexhaust line thereby passing the removed effluent through the sampleregion; detecting water vapor, nitric oxide, carbon monoxide, or ahydrocarbon by an absorption spectroscopy method by directing a lightbeam from a light source into the sample region through one or morelight transmissive window, wherein the light beam passes through thesample region and exits the sample region through one of the one or morelight transmissive window, and detecting the light beam exiting the cellthrough one of the one or more light transmissive window.
 75. The methodof detecting a gas phase molecular species according to claim 74,wherein water vapor is detected in the absorption spectroscopymeasurement method.